1. Field of the Invention
This invention relates to radiation blocking systems and in particular to methods and materials used as coatings to prevent document reproduction.
2. Description of Related Art
Photochromic materials, in particular the spiropyrans, are candidates for many light controlling applications such as, sun glasses, optical switches, Q switches, photochromic images, optical data processing and fast response filters to prevent the reproduction of documents. In the latter case the response speed of the filter should be faster than the time required to reach the threshold of detectability in the photosensitive element of the reproduction (e.g. photocopy) machine. The response times of certain spiropyrans are typically in the nano or pico second range when activated in a solution of a suitable solvent, but their conditioning into films or coatings typically requires the presence of a plastic binder which decreases considerably the reaction speed and prevents the reversibility of the phenomenon. The conditionment into film is otherwise necessary to the use of spiropyrans for preventing the reproduction of a document.
Accordingly, it is an objective of this invention to address at least some of the above noted difficulties.
Another objective of this invention is to develop radiation blocking materials that are photosensitive to the radiations utilized for the copying and/or reproduction of documents.
Still another objective of the present invention is to devise coatings or films capable of generating a blocking filter for said radiations in a time less than the time threshold of the recording photosensor.
A further objective of the present invention is to develop coatings or films capable of restoring original viewing transparency after the filtering action preventing the reproduction of a document.
Yet another objective of this invention is to develop coatings or films capable of blocking the radiations generated by conventional xerographic techniques to prevent the reproduction of a document without altering the readability of the document under normal viewing conditions.
A specific objective of this invention is the fabrication of coatings or films to prevent the reproduction of a document.